Light on push buttons went out and the ''service 4x4 went across the dash computer. Truck went into limp mode and won't go over 2000 rpm. Shut truck off and wait. Restart and same thing. Allison trans 8.1L engine ext. cab short bed.
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Re: '03 GMC 2500HD 4x4 problems
Take your positive cable off battery and wait a few minutes..This resets the computer and takes it out of limp mode.Theres been a lot of problems in the dash so if you can find an auto zone and have them scan it They'll do it for free.But as far as the lights my truck does the same thing. Just flick your fingers on the buttons and they should flash..The plug in the back of buttons was loose..
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!st of all, I really hope you are NOT driving on dry pavement with your 4x4 engaged. 2nd if you're trying to engage the 4x4 and your getting the service 4x4 light, it's telling you that it will not engage the 4x4. Hook up a code reader to your ECU and find out what's up. More than likely if you have the push button 4x4, your servo motor to engage the 4x4 is not working. If you're mechanically inclined buy a service manual and dig in, if not take it to the GM dealer before it becomes totally FUBARED
sometimes the plugs for the selonoids under the truck get wet and voids connections, you can check power at fuses and switch then down on actuators for the 4x4. My 90 has a floor shifter and if this is yours also then i'd check the linkage under truck for proper operation and shifting. My 03 yukon xl has the push button type on dash and everytime i get the truck washed at the car wash my 4x4 wont work for a day or two, as the plugs under truck get wet and shorts connections. I"m to lazy and it really doesnt bother me at the moment to climb under and dry and seal them so they are water tight.
I have the same exact truck as you do and had a similar problem awhile ago when i installed the hypertech system. I had to uninstall the hypertech and then have a buddy (cause i did not know how) drain the residual power from the brain... apparenlty the brain houses a small amount of power and remembers these codes so after you turn off your truck...poof there they are again. This worked for me, but then I had other electrical problems so I the dealership had to replace the brain.
safety[ limp] mode truck wont go over 2000 rmp but it will get u safely off road or to a service station or home ur getting some kind of code thats effecting ur truck --use a different reader urs might not be able to retrieve the problem code but can reset the computer-some auto stores such as auto zone / advanced auto scan for free check shops in ur local area
try to remove filter and pump out fuel from the tank. the gunk you loosened with "mechanic in a bottle" goes to filter then when ENGINE IS SHUT OFF GUNK SETTLES BACK IN LINE. NEED TO PUMP IT OUT TO SOLVE PROBLEM